It's a cool talk; you'll learn a lot about the pro and cons of each navigation structure, but at about 23 minutes in, while they were talking about the new nav drawer design, they dropped this slide and completely blew my mind:

YES.

That is an entirely new Gmail design - a new design rocking the awesome new navigation drawer. Let's take a look at this versus the current Gmail interface:

Ok, spot the differences! That's Leaked Gmail on the left and Current Gmail on the right.

First up is, of course, the navigation drawer. You can see the 3 line button in the top left (apparently called a "hamburger" by some Googlers) and the navigation drawer is currently open, which is covering (not pushing) most of the inbox. You can now easily switch between "Inbox" and "Priority Inbox;" in the current Gmail this requires a trip to the "All Labels" screen. The coolest part of this design is that you also now have top-level access to "All Labels," which is currently only accessible via a separate screen. The navigation bar will have to scroll, because this screenshot is missing core Gmail labels like Drafts, All Mail, Spam, and Trash.

It also looks like the bottom action bar is dead. If it was still around, you would see it in the bottom right, behind the navigation drawer, but the only thing there is more sweet vertical space for emails. The buttons that used to be there have found other places to call home: "Compose," "Search," and the overflow button are now in the top action bar, and the "All Labels" button isn't needed anymore, because everything is now in the navigation drawer. That only leaves "Refresh," which you could easily relegate to the overflow button, or pull-to-refresh, if Google wants to be really nice.

It's a shame we can't see more of the Inbox, but it looks like the stars are now much bigger. This screenshot has 24 hour time enabled, which is the cause of all the leading zeros on the timestamps. I don't see an easy way to switch accounts, but that could easily be added to the sidebar, which is what the freshly-redesigned Google Drive does.

I'm sure putting an I/O presentation together is a big rush, and this screenshot of the new Gmail accidentally ended up on there. The Googler giving the presentation, Jens Nagel, even accidentally included his @google.com email in the screenshot, which I have blurred out. (Dear Google, please be nice to him.)

Update: Why this is real

Some mockups are shown later in this talk, which has people questioning if this is real. So I'll give my reasoning:

The mockups weren't being shown at this point. Nothing is mentioned of Gmail being a mockup, and this slide is only used to generally talk about the navigation bar. Mockups are presented in sets, to talk about why they would or wouldn't chose that design. This "mockup" would have been completely wasted.

You wouldn't expose your personal information by having your real email address on a mockup.

If this was a mockup to demonstrate an alternative navigation format, you wouldn't arbitrarily change the size of the stars. You also wouldn't remove the bottom action bar.

Earlier in the talk, at around 12 minutes, they show a dogfood version of the Play Store (note the special icon). They just got sloppy with their screenshots.